A specialized Set implementation for use with enum types. All of
the elements in an enum set must come from a single enum type that is
specified, explicitly or implicitly, when the set is created. Enum sets
are represented internally as bit vectors. This representation is
extremely compact and efficient. The space and time performance of this
class should be good enough to allow its use as a high-quality, typesafe
alternative to traditional int-based "bit flags." Even bulk
operations (such as containsAll and retainAll) should
run very quickly if their argument is also an enum set.

The iterator returned by the iterator method traverses the
elements in their natural order (the order in which the enum
constants are declared). The returned iterator is weakly
consistent: it will never throw ConcurrentModificationException
and it may or may not show the effects of any modifications to the set that
occur while the iteration is in progress.

Null elements are not permitted. Attempts to insert a null element
will throw NullPointerException. Attempts to test for the
presence of a null element or to remove one will, however, function
properly.

Like most collection implementations, EnumSet is not
synchronized. If multiple threads access an enum set concurrently, and at
least one of the threads modifies the set, it should be synchronized
externally. This is typically accomplished by synchronizing on some
object that naturally encapsulates the enum set. If no such object exists,
the set should be "wrapped" using the Collections.synchronizedSet(java.util.Set<T>)
method. This is best done at creation time, to prevent accidental
unsynchronized access:

Implementation note: All basic operations execute in constant time.
They are likely (though not guaranteed) to be much faster than their
HashSet counterparts. Even bulk operations execute in
constant time if their argument is also an enum set.

copyOf

Creates an enum set initialized from the specified collection. If
the specified collection is an EnumSet instance, this static
factory method behaves identically to copyOf(EnumSet).
Otherwise, the specified collection must contain at least one element
(in order to determine the new enum set's element type).

of

Creates an enum set initially containing the specified element.
Overloadings of this method exist to initialize an enum set with
one through five elements. A sixth overloading is provided that
uses the varargs feature. This overloading may be used to create
an enum set initially containing an arbitrary number of elements, but
is likely to run slower than the overloadings that do not use varargs.

of

Creates an enum set initially containing the specified elements.
Overloadings of this method exist to initialize an enum set with
one through five elements. A sixth overloading is provided that
uses the varargs feature. This overloading may be used to create
an enum set initially containing an arbitrary number of elements, but
is likely to run slower than the overloadings that do not use varargs.

of

Creates an enum set initially containing the specified elements.
Overloadings of this method exist to initialize an enum set with
one through five elements. A sixth overloading is provided that
uses the varargs feature. This overloading may be used to create
an enum set initially containing an arbitrary number of elements, but
is likely to run slower than the overloadings that do not use varargs.

of

Creates an enum set initially containing the specified elements.
Overloadings of this method exist to initialize an enum set with
one through five elements. A sixth overloading is provided that
uses the varargs feature. This overloading may be used to create
an enum set initially containing an arbitrary number of elements, but
is likely to run slower than the overloadings that do not use varargs.

of

Creates an enum set initially containing the specified elements.
Overloadings of this method exist to initialize an enum set with
one through five elements. A sixth overloading is provided that
uses the varargs feature. This overloading may be used to create
an enum set initially containing an arbitrary number of elements, but
is likely to run slower than the overloadings that do not use varargs.

of

Creates an enum set initially containing the specified elements.
This factory, whose parameter list uses the varargs feature, may
be used to create an enum set initially containing an arbitrary
number of elements, but it is likely to run slower than the overloadings
that do not use varargs.

range

Creates an enum set initially containing all of the elements in the
range defined by the two specified endpoints. The returned set will
contain the endpoints themselves, which may be identical but must not
be out of order.

Type Parameters:

E - The class of the parameter elements and of the set

Parameters:

from - the first element in the range

to - the last element in the range

Returns:

an enum set initially containing all of the elements in the
range defined by the two specified endpoints